1. Field of the Invention
The present invention relates to a vehicle headlamp employing a semiconductor light emitting device as a light source.
2. Background Art
Light fittings, such as vehicle headlamps, sometimes need, for safety reasons, to form a light distribution pattern with high precision. The light distribution pattern is formed by an optical system employing, for example, a reflecting mirror or a lens.
In recent years, there has been proposed a vehicle headlamp (or light fitting) which employs a semiconductor light emitting element, such as a light emitting diode (LED), as a light source, and which is enabled to form a light distribution pattern that has a desired pattern shape and that provides a desired luminosity distribution (see, e.g., JP-A-2005-209538).
For example, as shown in FIG. 14, a light source unit 100 has an LED module 101, in which a light emitting diode device 102 serving as the light emitting element is mounted on a radiating board 103, and an LED mount 105 on which an LED module 101 is placed. The LED mount 105 regulates the lateral position and the rearward position of the LED module 101. The light source unit 100 also has a clip 107 which fixes the LED module 101 to the LED mount 105, a reflector 110 which reflects light emitted from the light emitting diode device 102 to the front of the light fitting, a lens 120 which projects light reflected by the reflector 110 to the front of the light fitting, and screws 130 with which the reflector 110 and the lens 120 are clamped together to the LED mount 105.
The reflector 110 is a substantially dome-like member fixed above the light emitting diode device 102. The reflector 110 has a substantially ellipsoidal reflecting surface, whose central axis is the optical axis of the light source unit 100, on the inner side thereof. With such a shape, the reflector 110 reflects light emitted from the light emitting diode device 102 to the front of a light fitting so that the reflected light converges to the optical axis of the lens 120.
The lens 120 includes a shade 122 provided at the side of the LED module 101. The shade 122 blocks or reflects a part of the light reflected by the reflector 110 to thereby cause light rays, which form the light distribution pattern of the light source unit 100, to be incident on a lens portion.
Meanwhile, the semiconductor light emitting element to be used as a light source for the vehicular headlamp is small. Thus, the light emitting region of the semiconductor light emitting element is narrow, as compared with those of conventional light sources. Accordingly, it is necessary for forming the light distribution pattern with high precision to assure the relative position of the light source with respect to the optical system with higher precision, as compared with the conventional case.
Thus, when the flat, plate-like heat radiating board 103, to which the light emitting diode device 102 is fixed, is fixed to the LED mount 105, a positioning projection 103e is provided on the heat radiating board 103 and is made to abut against an abutment portion 105a formed in the LED mount 105. Consequently, the heat radiating board 103 is positioned at the abutment portion 105a of the LED mount 105 with good precision in the horizontal direction.
Additionally, an assembling reference surface 106, which is used for determining the positions of the reflector 110 and the lens 120 with good precision in the direction of the optical axis, and a positioning projection 106a, which projects from a corresponding one of the assembling reference surfaces 106 substantially perpendicularly thereto, are provided at each of the front end portions of the LED mount 105. Each of the positioning projections 106a is engaged with a corresponding one of each of the positioning holes 110a and 122a respectively formed in the reflector 110 and the lens 120. Thus, the positions of the reflector 110 and the lens 120 in a direction perpendicular to the optical axis are determined with good precision.
However, even in the case of positioning the reflector 110 and the lens 120 using the assembling reference surface 106 and the positioning projection 106a provided at each of the front end portions of the LED mount 105 in the conventional light source unit 100, it is difficult for forming a high-precision light distribution pattern to assure sufficient relative position precision. Thus, high part precision and high assembling precision are required. The related vehicle headlamp has a problem that in the case of employing a semiconductor light emitting diode device 102 as a light source for a vehicle headlamp, the manufacturing cost thereof is increased.